The B-complex vitamins are an interesting group of essential micronutrients that are involved in energy production and blood building. Despite being required only in tiny amounts, they are vital for good health and performance. B-complex vitamins are water soluble, and most are not stored in the body for any length of time. This means they are safe to feed but also that a daily supply is necessary.
Pyridoxine (B6) and cobalamin (B12), folates and pantothenic acid have blood-building (hematopoietic) roles, and thiamine (vitamin B1), riboflavin (B2), niacin (B3), pyridoxine (B6), pantothenic acid and biotin have roles in energy metabolism.
Healthy horses on a mostly-forage diet produce their own internal supply of B-complex vitamins within the digestive tract via microbial fermentation. They also take in B-complex vitamins from pasture grass. Fermentation in the gut is the only way (apart from synthetic supplementation) that horses obtain vitamin B12, which is not produced in plants. Horses can manufacture their own niacin (B3). It’s not known, however, if they always produce enough of all the B-complex vitamins for optimal health and it is likely that working horses need more than they produce internally. Horses without healthy gut fermentation including those on antibiotics, and those fed too little fibre are also likely to be short of essential B-complex vitamins. Sick, ill and inappetant horses – especially those with liver challenges – and those under high levels of stress e.g. elite sports horses who travel extensively may also be short. Very young and very old horses are another group who may be deficient.
B-complex vitamins and particularly thiamine (B1) have been successfully used to boost appetite in hard-working or sickly horses, and are also thought to improve cellular energy production. Supplementation has also been shown to have a calming effect in some horses. Traditionally, vitamin B12 was commonly given to hard-working horses to enhance performance and avoid anaemia.
Brewers yeast is the richest natural source of B vitamins, and can be a very useful, palatable source that also has beneficial effects on the microflora of the digestive tract.
For a more reliable source with higher levels, look for a commercial product. Take care that your chosen product does not contain high levels of iron, which can be unhelpful for stressed or ill horses due to its pro-oxidant effect. Iron was traditionally used with B-complex vitamins for anaemia, but iron-induced anaemia is very rare in horses and iron supply from forage is usually plentiful.